Waste sulfite liquor recovery



April 27, 1954 H. o. GODDARD WASTE' SULFITE LIQUOR RECOVERY 7 Sheets-Sheet 1 Filed Apri; 2', 1949 ILT April 27, 1954 H. o. GODDARD WASTE SULFITE LIQUOR RECOVERY '7 Sheets-Sheet 2 Filed April 2 April 27, 1954 H. o. GODDARD wAsTE suLEITE LIQuoR RECOVERY 7 sheets-sheet s Filed April 2, 1949 April 27, 1954 H. o. GODDARD WASTE sULFITE LIQUOR RECOVERY 'April 27, 1954 H. o. GODDARD wAsTE SULFITE LIQUoR RECOVERY Filed April 2, ,1949

7 Sheets-Sheet 5 aibn Ouml Kmtmur INVENTOR Haro/al O. Gddarol ATTORNEY April 27, 1954 H. o. GODDARD WASTE suLFITE LIQuoR RECOVERY 7 Sheets-Sheet 6 Filed April 2, 1949V April 27, v1954 H. o. GODDARD WASTE suLFITE LIQUoR RECOVERY 7 Sheets-Sheet 7 Filed April 2, 1949 o d clara( Patented Apr. 27, 1954 UNITED STATES ATNT OFFICE Harold 0. Goddard, St. Catharines, Ontario, Canada Application April 2, 1949, Serial No. 85,116

This invention relates to the recovery of useful products from waste sulphite liquor discharged by sulphite pulp plants.

I-Ieretofore, numerous products have been recovered from waste sulphite liquor. For example, the sugars therein have been recovered and used in the production of alcohol. Sulphur dioxide gas and sulphites have been recovered from said liquor. Waste sulphite liquor has also been concentrated or dried and the liquor in concentrated or dried form has been burned. While prior recovery methods of which I am aware have been to some degree successful in accomplishing their purposes, they lhave not been economic in their functioning nor have they been trouble-free in their operation. l

The present invention provides a method of and apparatus for the recovery of useful products from waste sulphite liquor in which said products are economically recovered.

This invention also provides a method of and apparatus for concentrating waste sulphite liquor wherein a minimum of steam is used and a minimum of scaling of the concentrating apparatus occurs.

A method of and apparatus for producing a finely divided dried solid fuel useful, for example, as a fuel in a steam generator, is also provided by the present invention.

This invention also provides a waste sulphite liquor conversion method, and apparatus in which the sugars contained in waste sulphite liquor are economically converted intoV alcohol and in which the sugar denuded liquor is concentrated and dried.

In accordance with the present invention, steam for use in the operation of a sulphite pulp plant is generated to a pressure higher than that required for the operation of the digesters, paper machine dryers, or other steam consumers in said plant, and at the higher pressure is used to concentrate and to dry the waste sulphite liquor into va form which is usable as a fuel in a steam generator. The dry solids from the concentrated and dried waste sulphite liquor, which contain approximately 8,000 B. tl'u. per pound of dry solids, are produced, in accordance with the present invention, in a iinely divided state and may readily be substituted for pulverized coal to iire said steam generator. The steam, after use in concentrating and drying the waste sulphite lquor, is then used,`at its .reduced pressure, to operate the above-mentioned steam consumers of the sulphite pulp plant.` :Byv borrowing steam between the plant Vsteam generator and .the plant steam consumers, the waste sulphite liquor conversion is accomplished with a minimum of steam loss in evaporation.

Should it be desired to recover products other than dry, finely divided solids from the waste sulphite liquor, this may also be done by the method and apparatus of the present invention. For example, waste sulphite liquor, after it has been concentrated and the sulphur dioxide gas has been removed therefrom, is passed to apparatus for converting the sugars in the waste sulphite liquor to alcohol, the water and alcohol being evaporated from the waste sulphite liquor solids by steam from the plant steam generator. The

heat of Ythe alcohol and water vapors is used to l rectify the alcohol prior to conversion of said heat to usable steam in the steam consumers. The alcohol denuded liquor is concentrated and dried so that the above-mentioned finely divided dried product may be secured. A small alcohol plant which is economical in operation is thereby provided and a finely divided dried Vproduct usable for fuel is obtained.

The invention will be understood from the following description when considered in connection with the accompanying drawings forming a part thereof and in which:

Fig. 1 is a diagrammatic View of an arrangement of a portion of the apparatus of the present invention;

Fig. 2 is a continuation oi View shown in Fig. 1;

Fig. 3 is a diagrammatic view of another embodiment of the portion of the invention shown the diagrammatic in Fig. 2;

Fig. i is a diagrammatic view of an embodiment of the invention wherein waste sulphite liquor is treated with steam to prevent scaling of the evaporating apparatus;

Fig. 5 is a View similar to Fig. li but ci another embodiment of the invention;

Fig. 6 is a view similar to Figs. 4 and 5 but of a further embodiment of the invention;

`Fig. 7 is a partial View similar to Fig. 2 but showing an embodiment of the invention wherein alcohol is recovered from waste sulphite liquor,

yand

l ence numeral lc designates a digest-er of conventional construction which discharges through the bottom LIl thereof into a pipe l2 communicate ing with a discharge conduit I3. Steam for heating the contents of the digester to cooking temperature is conducted thereto from a steam generator shown diagrammatically at lli (Fig. 2) through steam line i5 and pipe i2 while sulphite acid used in the digester is introduced at the bottom thereof through pipes I6 and l2. Chips are conducted into the top of the digester through a conduit H.

.As is usual in the operation of such a digester, at the start of each batch the digester iii is loaded with wood chips conducted thereinto through conduit il and lilled with sulphite acid which enters the digester through pipes I6 and I2. The charge of wood chips and sulphite acid is then cooked by steam conductedV to the digester through lines l5 and l2. Upon completion of the cooking operation, the contents are discharged from digester il! into blow tank i8 through line l2 and discharge conduit i3.

Gases (SO2) flashed ofi during blow-down are vented from blow tank or pit lil through gas line Iii into a surface condenser 26 wherein vapor in the gas is condensed by flowing in contact with surface cooled by cool Waste sulphite liquor collected in a storage tank 2| during operation of the present invention as hereinafter described. The cool waste sulphite liquor is conducted to condense 2e through line 22 and, after condensing vapor in the SO2 gas and becoming heated by passing in heat exchange relationship with said gas, is passed to the upper part of an absorber 23 through conduit 2d. Condensate from condenser 2i? flows to hot Wash container 25 through line 2t while the SO2 gas, after the vapor has been removed therefrom, is passed to the lower part of absorber 23 through gas line 2l. Gases flowing into absorber 23 through gas line 21 are absorbed by waste sulphite liquor flowing into the absorber through conduit 2li. Any unabsorbed gases are Vented to the atmosphere from the absorber through outlet 28. The waste sulphite liquor, after absorbing SO2 in the absorber, hows to blow tank it through conduit 2t where it is mixed with the blown-down pulp from digester It to reduce the pulp consistency so that the samernay be pumped from said tank. The temperature of the pulp and liquor in blow-tank i8 would. normally be approximately 185 F. at which ternperature the SO2 therein would remain in solution.

The solution of pulp and Waste sulphite liquor is pumped from blo i tank i3 by puinp 2t' through line t@ into suitable pulp Washing apparatus such as rotary vacuum filters Si and 32 arranged in series. The washing apparatus would normally be designed to Wash approximately 90% or more of the waste sulphite liquor from the pulp with a dilution of less than one pound of water per pound of pulp and at the same time discharge liquor at the temperature at which it was received, that is, approximately 185 E. The mixture entering the washing apparatus through conduit E@ is Washed with a mixture of condensate from condenser which is discharged into iot wash container 25 through conduit 2G, and hot Water received from the evaporating apparatus hereinafter described. The condensate andY hot water mixture is pumped by pump 33 from container 25 through line 35 into the washing apparatus. Also hot Waterl from water storage Se, which water is received from evaporating apparatus hereinafter described, is pumped into the Washing apparatus by pump 56 through line 3l. Washed pulp is removed from the Washing ap- Gil paratus through outlet conduit 3'." while hot Waste sulphite liquor is passed from Washer 3| into hot waste sulphite accumulator 38 through line Waste sulphite liquor from washer 32 is recirculated to the Washer through recirculating lines 39 and @it by recirculating pump el. To maintain the proper pulp consistency in the washers and also in blow tank i il, a portion of the hot Waste sulphite liquor from accumulator 33 is passed to the washers through line 2 and to the blow tank through lines 2 and it by circulating pump fit. SO2 gas from accumulator 33 is conducted to absorber 23 through gas line i5 so that said gas will be scrubbed along with the gas entering absorber 23 through line l.

Waste sulphite liquor irom accumulator SS is pumped by pump 't5 through waste sulphite liquor conduit il to stripper evaporator apparatus Where said waste sulphite liquor is evaporated, cooled, condensed, concentrated and stripped of SO2 gas. Each stripper evaporator comprises a flash chamber and a condenser which are maintained under vacuum by means of a steam ejector.

The stripper evaporator, as shown in l, consists of four stages of evaporation indicated at A, E, C, and D. Each stage comprises a flash ychairdser and a condenser E@ both of which are maintained under vacuum by a steam ejector iii. Cooling medium for condensers 5u of stages A and B is provided from the cool Waste sulphite liquor storage tank 2i and flows through said condensers serially, passing into condenser or' B in line 52. After fiowing through condenser Se oi stage the Waste sulphite liquor flows to condenser 5@ or" stage A by way of line t thereafter passing through said condenser and outwardly therefrom into pipe 5t. Condensers 59 of stages D and C are supplied with a Water cooling medium which enters condenser Eil of stage D through cool Water conduit @il and passes through said -condensers serially, owing from condenser of stage D to condenser tit of stage C through line Si and from the condenser of stage C into hot water storage 35 through conduit 52.

. I-ot water for use in the pulp washing apparatus,

hereinbefore described, thusly provided.

From pipe Eil, the waste sulphite liquor is passed serially through condensers 56, said condensers communicating with one another through pipe 5l. Waste sulphite liquor from condenser bit flows to liash chamber :it ci stage A through conduit 5% while waste sulphite liquor from the hot waste sulphite liquor accumulator flowing through conduit lil' also passes to said flash chamber. The hot waste sulphite liquor from accumulator 3S and from the condensers 5e, Eil, and l is cooled and concentrated by successively liashing it through flash chambers fit o1 stages A, B, C, and D, the liquid from chamber d8 of stage A flowing therefrom to the flash chamber of stage B through line iii? in which chamber it is flashed` and passed to chamber it of stage C through conduit ln the flash chamber of stage l), the liquor flowing thereto 'through line 5t is and the remaining liquid flows to pump S5 through conduit Ei and is pumped to the cool waste sulphite liquor tank Zi through line ii'i.

The temperature of the Waste sulphite liquor owing through conduit il to flash chamber i8 of stage A would at substantially E'. While the waste sulphite liquor iiowing from "ondensers 565 into flash chamber' #i3 through oonduit 5t enters said flash chamber at approximately l6 l. VThe temperature of the waste sulphite liquor is progressively reduced by theash chambers 458 of stages A, B, C, and D so that the temperature of the liquor leaving ash chamber 48 of stage D through conduit |58 and passing to the cool waste sulphite liquor tank 2| through line 61 is at substantially 100 F.

The vapor flashed on in flash chambers 48 flows to the condenser 53 of the stage with which the chamber is associated through a line 68 thereafter to be condensed in said condensers 50. The condensate from condenser 50 of stage A is passed to condenser 50 of stage B through conduit 69 wherein it is iiashed and the condensate from condenserl 5d of stage B flows to hot wash container through line 1u. Condensate produced in condenser 50 of stage C is passed to condenser 5|) of stage D through conduit 1| and is flashed in the condenser of stage D. The condensate forming in condenser 5D of stage D is passed to hot water storage through line 12. In this manner, the heat contained in the condensate is recovered and the SO2 gas removed therefrom.

Steam line it is connected to each of the ejectors 5| of stages A, B, C, and D through steam conduits 'JS and 1li, steam conduit 13 being in communication with steam line l5 while conduit 14 is in communication with conduit 13. Ejector 5| of stage D receives steam from conduit 13 while the ejector of stages C, B, and A respectively, receive steam from conduit iii. The vapor removed from condenser of stage D by ejector 5i iiows through line i5 to condenser 58 of stage C wherein the condensibles are condensed and from which the vapor is withdrawn by ejector 5i for stage C. The vapors removed from the condenser for stage C by the ejector therefor are passed to condenser 58 of stage B wherein condensibles are condensed therefrom. Vapor withdrawn by ejector 5| of stage B flows to condenser 5d of stage A through line 11 and the condensible portion thereof is condensed in the condenser of stage A. The ejector of stage A discharges into condenser through line 18.

The non-condensibles from condenser 55, which comprises SO2 gas, is conducted through conduit 18' to the sulphite acid container for the plant, not shown, while condensate from condenser 55 flows through line 1d to condenser 50 of stage A wherein it is dashed. in the present invention, the steam ejectors 5i of stages A, B, C, and D serve a double purpose in that they maintain a vacuum on the hash chambers [i8 and condensers 5! of the stage with which they are associated and also build the pressure of SO2 gas back to a desired amount, for example, one pound per square inch gage. The ejector steam is condensed from the S92 gas in the various 'condensers so that a water saturated SO2 gas is released from the stripper evaporator` through conduit 18. It will be noted that in accordance with the method and apparatus of the present invention, the Waste sulphite liquor flowing to storage tank 2| through line 51 is concentrated without the use of auxilitary heat or excessive heating surfaces and that the SC2 gas is removed therefrom and reclaimed.

In accordance with the present invention, the Waste sulphite liquid in storage 2| may be further concentrated and also dried. As shown in Fig, 2 of the drawings, waste sulphite liquor from storage tank 2i of Fig. 1 is conducted through a conduit 8) to preheating apparatus comprising, as shown, three preheaters 8|, 82, and 83. The waste sulphite liquid in line d passes to a feed pump 84 which pumps the liquor into preheater.

. preheaters through valved 8| through line 85. From preheater 8 i, the liquor flows either to preheater 82 or to preheater 83 passing to preheater S2 through line 86 which is valved at 31 and S8 or to preheater 83 through line 88 and line 83 which is valved at 9i). Heated Waste sulphite liquor from preheater 32 passes into conduit 9| through valved line 92 while heated liquor from preheaters 33 hows into conduit 9| through valved line 93. From conduit 9|, the preheated waste sulphite liquor passes into conduit 9d thence through a circulating pump 95, which places the liquor under pressure into a plurality of heaters 8E through a feed line 91 in which heaters the liquor is heated un.. der pressure. Each of t e heaters dd receives feed from line 91 through valved connections 88 and discharges the heated waste sulphite liquor through valved outlet connections @9 into an outlet conduit |08. Heated Waste sulphite liquor from the conduit |09 is passed to a steam converter il. Converter It! is under such lower pressure than the heaters that the waste sulphite liquor is flashed into steam some of which steam is condensed and the remainder of which is removed from the converter in a vaporous state.

As shown, steam from the converter lil flows outwardly therof and into steam line l5 through conduit |82'. A portion of the steam in line |82 is passed through conduits |@3 and Hill to preheaters 82 and 88. Steam enters preheater 83 through line lll-t which line is vaived adjacent the preheater while steam flows to preheater 82 through conduit ltd through connection |85 which connection is valved. It will be noted that the various steam connections and waste sulphite liquor connections to preheaters 82 and 83 are so valved that one of the heaters may be disconnected from the circuit and cleaned without interfering with the functioning of the other preheaters. '-ieaters @t receive steam for the heating of the waste sulphite liquor iiowing thereinto through lines Si' and Q8 from a steam conduit |86- which receives steam from steam line i5, the steam from conduit itt iiowing into said connections |01. Condensate from heaters Qt passes into a concondensate line li through valved connections |09, said condensate thereafter passing to a secondary steam converter Elli which is under such pressure that part of the condensate flashes into steam. Steam from converter Hl! also flows into steam converter Il@ through lines it? and |93 and, by heat interchange in secondary converter |8 flashes additional condensate from heaters 98 entering said converter through line |88 into steam. The remaining condensate is returned from converter im through line |29 to steam generator Ul. Con-densate from the preheaters 82, and 83 flow through valved connections into condensate line H2 which is connected to receive condensate from secondary steam converter H8 and connects with a conduit iid conducting condensate from preheater di to a flash chamber ||i.

In operation, the waste sulphite liquor nov/ing into feed pump gli through conduit de is brought up to the operating pressure of steam converter |0| and passed into preheater di through line 85. From preheater 8|, the waste suiphite liquor is conducted to either or both ci the preheaters 812 or 83, and after heating therein is conducted to the heaters Qt through either or both lines 92 and 93 into line 9| and from line si through conduit S4, circulating pump 95, and line .91. From line 91, the lpreheated. waste sulphite liquor is conducted to any one or all of the heaters S5 through connections 93. After heating in the heaters 95, the Waste sulphite liquor is passed into lines It@ through outlet connections 99 thence into the steam converter itl. lt will be noted, that the inlet connections and the outlet connections 99 are so valved that any one or ail of the heaters be used and Various heaters may be removed from the line for cleaning as desired. Preheating in the preheaters Si, 32 and S3 and the heating in heaters Sii ie done under pressure to avoid steaming in the Waste sulphite liquor so as to reduce the scaling on the preheater and heater surfaces. As shown, the liquid level in steam converter Ici is controlled by capacity control valve IIB in line ei while the pressure in said stearo converter' is controlled by pressure control valve H5 inline ISG.

After removal of vapor therefrom in converter Il, a portion or the waste sulphite liquor of the desired concentration is Withdrawn from the bottorn of steam converter It! through outlet conduit Hl controlled by a specific gravity control valve Ii which controls the specific gravity of liquor flowing through outlet line li?. Another portion of the waste sulphite liquor of the desired concentration nous irorn the steam converter iI through line Si, in which it is diluted by waste sulphite liquor entering said line through conduit 9 I, and is thereafter pumped by circulating pump 95 into the heaters Q6. The flashing of the waste sulphite liquor in steain converter iti provides calcium sulphate crystals wi ich have surfaces suiiiciently large that the scaling of heaters by said liquor passing thereinto through lines te, 9i and Qt will be reduced. These crystals will have a gentle scouring action to remove any scale adhering to the tubes and. Wili prevent supersaturation of caiciuxn sulphate in the heater tubes by oiering a surface on which the calcium sulphate will tend to iirst crystallize and Will prevent supersaturation or caiciurn sulphate in the steam converter iilI.

Concentrated Waste from steam converter itil through line passed to a dryer fis shown in Fig. 2, the dryer IIS comprises a rotating drum ld across the face of which an even iilin of concentrated Waste sulphite liquor iron line il? is distributed by distributor 132i. Steam from steam converter Ii flowing through lines iiii. and it pass into the drum l2@ so as to heat the outer periphery thereof through line Ef. The heat of the steam is such that the nin?. oi concentrated Waste sulphite liquor will ce drie-:l into solid orrn in one revolution oi the the dry solids will thereafter be removed from said surface by a scraper or other desirable means. The dried solids which comprses d ded dry some nat si'nilar to pulycrised coal are removed from the by a screw conveyer rotary air-loch, not shown, and passed into line Stil', which, as shown, is connected to burners of steam generator it. The liti is so enclosed that the vapor released roin the waste sulpliite liquor in drying may be conducted through a pipe to preheater 5i thereby used to preheat sulphite liquor lot-fog into said heater. The condensa-te thedryer lio into ii through line Sit, together with the cond nsate from heater Bi, flows thrcugr line H3 into fia-sh chamber iil. ber hows into cc neer t (Fig. i) through conduit IE5 w .iie the condensate from said nach chamber is pumped by pump 26 through line 427 sulphite liquor iiowing iii The steam iroin hash chariinto condenser EE. The condensate from condenser 55 oWs from condensate line |28 into line 79 which, as heretofore described, extends between condenser 55 and condenser 5@ of stage A.

As shown in Fig. 2, steam from steam converter HEI passes through lines it and ID3 into secondary steam converter No from which converter condensate passes into preheaters t2 and S3 through line I I2 as hereinbeiore described. Condensate from converter i id also i'iows to the steam generator I4 through conduit IQQ. Steam from secondary converter i l is passed to steam consumers such as paper machines through steam conduit ISB.

The Waste sulphite liquor from storage 2i may be dried by means of drying apparatus other than the drum dryer I Iii or Fig. 2. As shown in Fig. 3, waste sulphite liquor frein storage tank 2i iiows into the suction side of reed pump Sii through line Si! and is fed by said puinp through line 85 into a preheater el. From prelieater 8l', the

heated waste suiphite liquor is passed through conduit 53 to preheater E32 Where it is further heated prior to passage thereof through line I33 into the upper part oi a scrubbing tower i353. rlhe scrubbing tower is used to scrub gases entering the lower part thereof by passing the gases which flow upwardly in the tower countercurrent to and in contact with the heated Waste sulphite liquor which passes downwardly in the tower. The scrubbed gases are Vented through a vent pipe E35 While the waste sulphite iquor, after use in scrubbing gases, is pumped. from the lower portion of tower i3d by puinp its through line It? into preheater ti. Preheaters ti, 82 and t3 are arranged slightly diii'erently than in Fig. 2 inasinuch as the waste sulphite iiquor is heated by the passage thereof sa ally through the heaters. That is, from the preheater 8 i, heated Waste sulphite liquor passes to heater i2 through line -S and after the heating thereorn in preheater is passed to preheater 33 through line S2. Waste sulphite liquor heated in the heaters SI, and 33 is then passed from 3 into line thence into conduit t! i. The heating inediiun for preheaters 8i, 8E', and S3 is condensate from secondary steam converter i it which condensate is passed through heaters serially and enters preheater gli through condensate line H2. Con- I- 1% The to use i to t2 through line and after use in oreheate is passed to preheater Sii through line condensate from preheater 8i is conducted preheater 8i through conduit i333 and after in preheater 8i is condmtefn through line ii hot Wash tank 25 (Fig. l)

The Waste sulphite liquor in conduit 9i flows into conduit Sii and is pumped by pump 95 into line tl whence it passes into heaters 93, as hereinbefore described in the description o the ern bodiinent of the invention shown in. Fig. 2. After heating in heaters 9F, the Waste sulphite liquor is passed through outlet conduit te@ to the steam converter iti which converter is under such pressure that the Waste sulphite liquor is ashed into stearo sonic of which is condensed and the remainder of which is removed roin the converter as rEhe operation of the converter is the same as in the embodiment of the invention shown in 2. The steam, however, passes upwardly from the converter through lines ISE, and into secondary steam converter i I) while waste sulphite liquor oi the desired concentration is withdrawn from the bottom of steam converter It-I through outlet vconduit H7 `controlled by a 9 specific gravity control valve H8 and is introduced into a flash tank |39. In the flash tank |3t, the waste sulphite liquor is further concentrated by the removal of steam therefrom, the steam iowing from the dash tank through conduit lle into preheater |32 wherein it is used to heat the waste sulphite liquor flowing to scrubbing tower |34 through lines ll' and |33. The condensate from preheater |32 fiows into condensate line |38 between preheaters 8| and 8| through conduit |4|. Concentrated waste sulphite liquor from ash tank |39 passes into a spray dryer |62 through outlet conduit l, conduit |43 being connected to rotary spray head or atomizer ldd revolved at a high speed by a motor |45. The spray from atomizer |44 is dried by flue gases from steam generator Hl which is conducted to the dryer |42 through nue lil. By drying the Waste sulphite liquor in the spray dryer, calcium sulphate solids somewhat similar to pulverized coal are formed, which solids are removed from the drying gases by cyclones |45 in the dryer lll?. The solids after separation from gases pass downwardly and outwardly of the dryer through outlet pipe i'i, controlled by an air-lock |48, and into a fuel feed pipe M9. The solids are carried through feed pipe |133 into a steam boiler Hl through a burner |55 in an air stream provided by fan |5|.

Gases separated from solids by the cyclones in dryer |42 are removed by a fan |52 which withdraws said gases from the dryer through outlet pipe |53 and introduces said gases into scrubbing tower |36 through gas inlet |56. As hereinlcefore set forth, the gases are scrubbed in tower |34 by passing them countercurrent to and in Contact with the waste sulphite liquor flowing into the top of the tower through line |53 and downwardly in the scrubber.

While it is highly desirable to flow waste sulphite liquor from accumulator 38 through the multiple stripper evaporators as hereinbefore described, it is possible to obtain a dried solid by conducting hot waste sulphite liquor from accumulator 33 to steam converter |G| of Figs. 2 and 3 through conduit 2t@ indicated by dot and dash lines in Figs. l, 2, 3 and 7. Concentrated waste sulphite liquor so conducted to converter would thereafter be dried as hereinbefore set forth in the description of Figs. 2 and 3.

So that the waste sulphite liquor flowing from the preheaters to heaters 95 through lines 9| and S4 in Figs. 2 and 3 and thence to converter lill through line |60 may have avhigh solution of calcium sulphate therein, it may be desirable to precipitate said calcium sulphate by treating the preheated waste sulphite thereby minimizing or preventing formation of scale in the heaters $6 and in the converter lil. In the embodiment of the invention illustrated in Fig. 4, the waste sulphitc liquor iovving from the preheaters, only two of which are shown in Fig. 4, is passed into a treatment tank |55 through line 9|. In the treatment tank |55, the waste sulphite liquor is `treated by steam which is introduced into said tank through steam line |55 which receives live steam from steam line i5 through conduit it. Treatment by steam in tank |55 precipitates the calcium sulphate in the waste sulphite liquor prior to the passage of said liquor from tank |55 into line 9|' thence into conduit gli. Scaling of the heaters Q6, only one of which is shown in Fig. 4, is thereby greatly minimized or prevented.

The form of the invention shown in Fig. 5 is somewhat similar to that shown in Fig, 4, but a further treatment tank is positioned in the line leading from heaters 96 to converter lil A treatment tank |51 is positioned in outlet conduit |00 so that heated waste sulphite liquor from heater or heaters flows into said treatment tank which is similar to treatment tank |55. Steam for precipitating calcium sulphate in the waste sulphite liquor delivered in tank |57 through line lill! is received by said tank from steam line l5 through lines |05 and |58. After calcium sulphate is precipitated from the waste sulphite liquor in tank |57, the liquor is passed into the upper portion of steam converter |0| through line |93.

In the embodiment of the invention shown in Fig. 6, waste sulphite liquor flowing from the preheaters to the heaters 96 through lines 9|', 9G, 91 and S2 is treated by steam from steam converter iii! to precipitate the calcium sulphate in said liquor. As shown, steam which passes from steam converter itl through conduit |02 flows to secondary steam converter iid through line |03 as hereinbefore set forth in the description of the embodiment of the invention shown in Fig. 2. Some of the steam from line HB3 is passed through conduit |5 (Fig. 6) to treatment tank 55 wherein it is used to precipitate the calcium sulphate in the waste liquor passed into said treatment tank through line e l. After treatment, the Waste sulphite liquor is passed throughlines Si ed and pump 95, thence through lines al and 98 into heater 9E, as set forth in the description relating to the embodiment of the invention shown in Fig. 4. In this manner, scaling of the heaters 96, only one of which is shown in Fig. 6, is prevented.

The waste sulphite liquor in tank 2| may also be used for the production of alcohol as well as fuel. In the embodiment of theinvention shown in Fig. 7, cooled waste sulphite liquor from tank 2| is passed to alcohol fermenter ie@ wherein fermentation is carried out in the usual way with a suitable distilling yeast. Nutrients necessary for supporting of the yeast is also supplied. 'After fermentation, the fermented waste sulphite liquor flows through conduit Sil' into suction feed pump 84 thereafter to be discharged from said pump into preheater 8| through conduit 85. After becoming heated in preheater 3|, the uid is passed through line 86 to preheater 82 wherein it is further heated and thereafter passed through conduit 92 into preheater 83. Heatedfluid from preheater 83 flows into conduit 9| and passes into steam converter ||l| which is similar to the converter shown in Figs. 1 to 6.

In converter mi, the fluid is vaporized, a portion of the vapor passing outwardly of the converter through lines |02 and |03 while another portion thereof is condensed. A part or the condensed portion passes outwardly thereof through conduit 94 and is pumped by pump e5 through conduits 91 and S8 into heaters $6, as set forth in the description relating to the embodiment of the invention shown in Fig. 2, the heated fluid flowing from the heaters 9B into converter ||l| through line |00. As in the form of the invention shown in Fig. 2, a concentrated portion of the condensed fluid from converter |02 flows through line into drum-type dryer l i9.

The vapor flowing outwardly of converter lill through lines |92 andlll passes into the lower portion of a rectifying column USI, a portionV of said vapor being conducted to dryer I9 through line |22 for use as a heating medium in thedryer. Condensate formed in dryer i9 is pumped therefrom by pump |24' through line |24 which disl l charges it into conduit E62. Conduit E62, in turn, discharges the condensate into the upper part oi rectifying column ESS. In rectifying column 25|, the condensate ilows downwardly through vapor and liquid contacting devices ISI passing coun- 'tercurrent to and in contact with the vapor discharged into the lower part of said column through line its. Vapor from the rectifying column ows outwardly thereof through vapor conduit |53 and into secondary steam converter Hit. A part of the condensate formed in secondary steam converter H0 passes therefrom into line H2 and is discharged into the upper Vpart of rectifying column |6| wherein said conu Vdensate passes downwardly countercurrent to and in contact with the vapor passing upwardly within the column. The remainder oi the condensate from converter i lil flows through conduit |29 to the boiler ll.

Vapor from secondary steam converter l it passes through vapor conduit ld into the lower portion of another rectifying column 65. In rectifying column l said vapor flows upwardl through vapor and liquid contact devices |55 within the column countercurrent to and in con tact with condensate which enters the upper part of column |555 through line it which line rcceives said condensate from preheater i. Waste sulphite fluid from iermenter it@ which enters preheater Ei through line 85 is heated in said preheater by vapor from rectifying column it iiowing thereinto through conduit V55. The condensate from the vapor flows from said preheater through line |56 and is returned to said column as hereinbefore described. Alcohol is withdrawn from column |65 'through conduit |67 and insel oil is removed from the column through conduit |68. Condensate is pumped from the lowerpart of column 55 by pump |69 which receives Vsaid condensate through pipe |10 connected at one end thereof to the bottom of said column and at the other end to the suction of said pump. Pump |69 provides pressure to pump the condensate from column E65 to the upper part of rectifying column I6! through conduit 51|, said condensate theerater passing downwardly in the column countercurrent to and in contact with the vapor iiowing upwardly therein.

Preheater 83 is heated by condensate which it `receives through line |12 connected to said preheater and the lower part of rectifying Ycolumn 16| The condensate from said preheater is discharged therefrom through line |13 into dash chamber im which is similar to flash chamber ||4 of Fig. 2. Preheater 82 receives vapor from dryer H9 through line |23, the condensate from preheater 82 being discharged into line H3 through pipe ill-i and vapor from said preheater being discharged into steam outlet conduit from flash chamber IM. The steam outlet conduit from flash chamber I4, as in the form ci the invention shown in Fig. 2, discharges into condenser 5S of Fig. l, while condensate from flash chamber lll is passed through line |27 by pump |26 into condenser 55.

With the embodiment of the invention shown in Fig. 7, alcohol distillation from waste sulphite liquor removed from a mixture received from a digester and concentrated, as shown in Fig. l and dried as illustrated in Fig. 2, is accomplished without the necessity of using extra steam for distillation. This results in a more efficient use of steam and a great reduction in the steam cost for distillation.

It will be apparent that various modifications may be made in the form of the apparatus herein disclosed and in the steps of the process herein described without departing from the spirit of the invention which is Vnot to be limited excepting by the scope of the appended claims.

What is claimed is:

l. lh a sulphite pulp plant comprising a steal. generator, steam conduit means for conductin,v steam from the steam gen rator, a digester ted to receive a nin-ous substance, suiphite cooking iiduor and steam from the steam generator, means for hlowingdown said digester, separating meal adapted to separate iihrous suostance and cooking liquor, means for conducting the m" ture blown-down from the digester to tia, sepasc means, a plurality of evaporators each having an evapcrating Zone, concentrate conduit means for connecting said evaporators in series so that concentrate is conducted from one :.porator to the evaporating zone of the next succeeding evaporator, a condenser communicat ing with each evaporator so as to receive conishie medium :iereirom, said condensers hee adapted for the passage of a cond ng mediie medium in indirect heat 'fe relationship with one another, means ting said condensers in series so as to cons-.id heat exchai relationship with said condensiole medium one condenser from the one condenser to the .next succeeding condenser, vacuum producing means cooperating with each the evaporators and condensers to maintain the same under vacuum and evaporate he liquor conducted to said evaporators, waste sulphite liquor conducting means in communication with said separating means so as to receive separated therefrom and in communi-cation with evapor zone of the first of a series of evaporators to conduct said liquor thereto, concentrate receiving means, means in communication with the last of said series ci evaporators and with the concentrate receiving means, concentrate conducting means in communication with the concentrate receiving means and the rst of a of oondensers so as to conduct the concentrate to said first condenser for use as a condensing medium therein, and a used concenrate conduit in communication with the last of said series ci condensers and the first of said series oi evaporator-s so as to receive said used concentrate after use thereof as a condensing in said last condenser and to conduct it to the evaporating zone of said first evaporator.

2. In a suplhite pulp plant comprising a steam generator, steam conduit means for conducting steam from the steam geneator, a digester adapted to receive a fibrous substance, sulphite cooking liquor and steam from the steam generator, means for blowing-down said digester, washing means adapted to wash iibrous substance from cooking liquor, means for conducting the mixture blown-down from the digester to the washmeans, a plurality of evaporators each having an evaporating zone, concentrate conduit means for connecting said evaporators in series so that concentrate is conducted from one evaporator to the evapora-ting sone of the next succeeding evaporator, a condenser communicating with each evaporator so as to receive condensible medium therefrom, said condensers being adapted for the passage of a condensing medium and a condensible medium in indirect heat exchange relationship with one another, means connecting said condensers in series so as to conduct conmaracas 13 densing medium after passage thereof in said heat exchange relationship with said condensible medium in one condenser from the one condenser to the next condenser, vacuum producing means cooperating with each of the evaporators and condensers to maintain the same under vacuum and evaporate the liquor conducted to said evaporators, Waste suiphite liquor conducting means in communication with said washing means so as to receive separated liquor therefrom and in communication with the evaporating zone of the rst of a series of evaporators to conductv said liquor thereto, concentrate receiving means, means in communication with the last of said series of evaporators and with the concentrate receiving means, concentrate conducting `means in communication with the concentrate receiving means and the rst of a series of said condensers so as to conduct the concentrate to said rst condenser for use as a condensing medium therein, condensate conducting means in communication with the condensers and with Washing means so as to conduct said condensate from the condensers to the washing means, and a used concentrate conduit in communication with the last of said series of condensers and the rst of said series of evapcrators so as to receive said used concentrate after use thereof as a condensing medium in said last condenser and to conduct it to the evaporating Zone of said first evaporator.

3. In a sulphite pulp plant comprising a steam generator, steam conduit means for conducting steam from the steam generator, a digester adapted to receive a nbrous substance, sulphite cooking liquor and steam from the steam generator, means for blowing-down said digester, a blow-down receiver in communication with the digester to receive a mixture of brous material and cooking liquor therefrom, an absorber so arranged that a gas and a liquid are passed in ,Contact With one another, a gas line in communication with the absorber and with the digester blow-down receiver to receive gases therefrom, absorbing liquid conduit means in communication with the absorber and with said blow-down receiver so as to conduct liquid from the absorber to said receiver, washing means adapted to Wash fibrous substance from cooking liquor, means for conducting said mixture from the blovvdovvn receiver to the Washing means, a plurality of evaporators each having an evaporating sone, concentrate conduit means 'for connecting said evaporators in series so that concentrate is conducted from one evaporator to the evaporating zone of the next succeeding evaporator, a condenser communicating with each evaporator so as to receive condensible medium therefrom, said `condensers being adapted for the passage of a tors, Waste sulphite liquor conducting means in communication With said washing means so as to receive separated liquor therefrom and in com..

munication With the evaporating zone of the first of a series of evaporators to conduct said liquor thereto, concentrate receiving means, lmeans in communication with the last of said series of evaporators and With the concentrate receiving means, concentrate conducting means in communication with the concentrate receiving means and the iirst of a series of said condensers so as to conduct the concentrate to said first condenser for use as a condensing medium therein, other concentrate conducting means in communication with said concentrate receiving means and with the absorber so as to conduct concentrate to said absorber, condensate conducting means in communication with the condensers and with said Washing means so as to conduct said condensate from the condensers to the Washing means, and a used concentrate conduit in communication with the last of said series of condensers and the first of said series of evaporators so as to receive said used concentrate after use thereof as a condensing medium in said last condenser and to conduct it to the evaporating zone of said first evaporator.

4. In a sulphite pulp plant comprising a steam generator, steam conduit means for conducting steam from the steam generator, a digester adapted to receive a nbrous substance, sulphite cooking liquor and steam from the steam generator, means for blowing-down said digester, a

low-down receiver in communication with the digester to receive a mixture of iibrous material and cooking liquor therefrom, a blow-down vapor condenser in communication with the blow-down receiver so as to receive vapor therefrom, said blow-down vapor condenser being adapted to receive a condensing medium and a condensible medium for passage in indirect heat exchange relationship with one another, an absorber so arranged that a gas and a liquid are passed in contact with one another, a gas line in communication With the absorber and with said blow-down vapor condenser so as to receive uncondensed vapor therefrom, absorbing liquid conduit means in communication with the absorber and with said blow-down receiver so as to conduct liquid from the absorber to said receiver, separating means adapted to separate iibrous substance from cooking liquor, means for conducting said mixture from blow-down receiver to the separating means, a plurality of evaporators each having an evaporating zone, concentrate conduit means for connecting said evaporators in series so that concentrate is conducted from one evaporator to vthe evaporating zone of the next succeeding evaporator, a condenser in communication with each evaporator so as to receive condensible medium therefrom, said last-mentioned condensers being adapted for the passage of a condensing medium and a condensible medium in indirect heat exchange relationship with one another, means connecting said last-mentioned condensers in series so as to conduct condensing medium after passage thereof in heat exchange relationship With said condensible medium in one of the last-mentioned condensers from said one condenser to the next succeeding condenser, vacuum producing means cooperating with each of the evaporators and condensers to maintain the same under vacuum and evaporate the liquor conducted to said evaporators, Waste sulphite liquor conducting means in communication With said separating means so as to receive separated liquor therefrom and in communication with the 4evaporating zone of the rst of a series of evaporators to conduct said liquor thereto, concentrate receiving means, means in communicawith the concentrate receiving means, concentrate conducting means in communication with the concentrate receiving means and the rst of said last-mentioned condensers so as to conduct the concentrate to said rst condenser as a condensing medium therein, other concentrate conducting means in communication With said concentrate receiving means and with the blow-down vapor condenser, a connection between said blow-x down vapor condenser and said absorber arranged to conduct concentrate as a condensing medi in in said blow-d wn vapor condenser to the absorber for use as absorbing liquid therein, a condensate line in communication with the blow-down condenser with said separating means to conduct condensate from the blowdown condenser to the separating means for use as a seperatii f Fluid the An, and a used concentrate conduit in communication with the last of the aforesaid iast-menticned condensers and the first of said plurality of evaporators so as to receive said used concentrate after use thereof as a condensing medium in said last condenser and to conduct it to the evaporating zone of said first evaporator.

5. a sulphite pulp plant comprising a steam generator, steam conduit means for conducting steam from the steam generator, a digester adapted to receive a fibrous substance, sulphite cooking liquor and steam from the steam generator, means for blowing-down said digester, separating means adapted to Wash iibrous substance from cooking liquor, means for conducting the mixture blown-down from the digester to the Washing means, a plurality of evaporators each having an evaporating zone, concentrate conduit means for connecting said cvaporators in series so that concentrate is conducted from one evaporator to the evaporating Zone of the next succeeding evaporator, a condenser in commanica-tion with each evaporator so as to receive condensible medium therefrom, said condensers being adapted for the passage of a condensing medium and a condensiole mediumv in indirect heat exchange relationship With one another, connecting said condensers in series so as to conduct condensing medium after passage thereof in said heat exchange relationship with condensible medium in one condenser from the one condenser to the next succeeding condenser, vacuum producing means comprising a steam iet cooperating with each of the evaporators and condens-ers to maintain the same under vacuum and evaporate the liquor conducted to said evaporators, a iive steam line communicating with said conduit means and with the steam discharge steam lines connected to each of said steam ts and with condensers of said series of condensers to conduct steam discharged from the steam ,iets to said condensers, condensed steam lines communicating with the condensers and with said sepa-rating means to conduct condensed steam from the ejectors and condensed vapor from the evaporators to said separating means for use therein, waste sulphite liquor conducting means in communication with said separating means so as to receive separated liquor therefrom and in communication with the evapora-ting zone of the first of said plurality of evaporators to conduct said liquor thereto, concentrate receiving means, means in communication with the last of said plurality of evaporators with the concentrate receiving means, concentrate conducting means in communication with the concentrate receiving means and the rst of a series of said condensers so as to conduct .the concentrate to said rst condenser for use 1, 6 as a condensing medium therein, and a used concentrate conduit inV communication with the last of said series of condenseis and the first of said series of evaporators so as to receive said used concentrate after use thereof as a condensing medium in said last condenser and to conduct it to the evaporating zone of said first evaporator.

6. In a sulphite pulp piant comprising a steam generator, steam conduit means for conducting steam from the steam generator, a digester adapted to receive a brous substance, sulphite cooking liquor and steam from the steam generator, means for blowing-down said digester, a blowdown receiver in communication with the digester to receive a mixture of fibrous material and cooking liquor therefrom, a blow-down vapor condenser in communication with the blow-down receiver sov as to receive vapor therefrom, said blow-down vapor condenser being adapted to receive a condensing medium and a condensible mediumfor passage in indirect heat exchange relationship with one another, an absorber so arranged that a gas and a liquid are passed in contact with one another, a gas iine in communication with the absorber and with said blowdown condenserl so as to receive uncondensed vapor therefrom, absorbing liquid conduit means in communication with the absorber and with said blow-down receiver so as to Conduct liquid from the absorber to said receiver, Washing means adapted to Wash fibrous substance from cooking liquor, means for conducting said mixture from the blow-down receiver to the Washing means, a plurality of evaporators each having an evaporating zone, concentrate conduit means for connecting said evaporators in series so that concentrate is conducted from one evaporator to the evaporating zone of the next succeeding evaporator, a condenser in communication with each evaporator so as to receive condensible medium therefrom, said last mentioned condensers being adapted for the passage of a condensing medium and a condensible medium in indirect heat exchange relationship with one another, means connecting said last-mentioned condensers in series so as to conduct condensing medium after passage thereof in heat exchange relationship with said condensible medium in one of the last-mentioned condensers from said one condenser to the next succeeding condenser, vacuum producing means comprising a steam jet cooperating with each of the evaporators and condensers to maintain the saine under vacuum and evaporate the liquor conducted to said evaporators, a live steam line communicating With said steam conduit means and with the steam jets, discharge steam lines connected to each or" said steam jets and with condensers of said series of condensers to conduct steam discharged from the steam jets to said eondensers, condensed steam lines coinmunicating with the condensers and with said Washing means to conduct condensed steam from the ejectors and condensed vapor from the evaporators to said washing means for use therein, Waste sulphite liquor conducting means in communication with said Washing means so as to receive separated liquor therefrom and in communication with the evaporating zone of the rst of a series of evapora-tors to conduct said liquor thereto, concentrate receiving means, means in communication With the last of said series of evaporators and with the concentrate receiving means, concentrate conducting means in communication With the concentrate receiving means and the` first of said last-mentioned condensers so as to conduct the condensate to said first condenser as a condensing medium therein, other concentrate conducting means in communication with said concentrate receiving means and with the blow-down vapor condenser, a connection between said blow-down vapor condenser and said absorber arranged to conduct concentrate used as a condensing medium in said blow-down vapor condenser to the absorber for use as absor-bing liquid therein, a condensate line in communication with the blow-down condenser and with said Washingmeans to conduct condensate from the blow-down condenser to the washing means for use as a wash iiuid therein, and a used concentrate conduit in communication with the last of the aforesaid last-mentioned condensers and the first of said plurality of evaporators so as to receive said used concentrate after use thereof as a condensing melium in said last condenser and to conduct it to the evaporating zone of said nrst evaporator 7. In a sulphite pulp plant comprising a digester adapted to receive a fibrous substance, sulphite cooking liquor and steam, means for blowing down said digester, separating means adapted to separate fibrous substance and cooking liquor, means for conducting the mixture blown-down from the digester to the separating means, a plurality of evaporators each having an evaporating zone, concentrate conduit means for connecting said evaporate in series so that concentrate is conducted from one evaporator to the evaporating rone of the next succeeding evaporator, a condenser communicating with each evaporator so as to receive condensible medium therefrom, said condenser being adapted for the passage of a condensing medium and a condensible medium in indirect heat exchange relationship with one another, vacuum producing means cooperating with each of the evaporators and condensers to maintain the same under vacuum and evaporate the liquor conducted to said evaporators, Waste sulphite liquor conducting means in communication with said separating means so as to receive separated liquor therefrom and in communication with the evaporating zone of the first of a series of evaporators to conduct said liquor thereto, concentrate receiving means, means in communication with the last of said series of evaporators and with the cencentrate receiving means to conduct concentrate from said last evaporator to the receiving means, concentrate conducting means in communication With the concentrate receiving means and said condensers so as to conduct concentrate to said condensers for use as a condensing medium, and a used concentrate conduit in communication with the first of said series of evaporators and with the condensers so as to receive concentrate from said condensers after use as a condensing medium and conduct it to said first of the series of evaporators so as to receive said used concentrate after use thereof as a condensing medium in the condensers and to conduct it to the evaporating zone of said first evaporator.

8. 1n a sulphite pulp plant comprising a digester adapted to receive a fibrous substance, sulpbite cooking liquor and steam, means for blowing down said digester, a blow-down receiver in communication with the digester to receive a mixture of nbrous material and cooking liquor therefrom, an absorber so arranged that a gas and a liquid are passed in contact with one another, a gas line in communication with the absorber and with the digester blow-down receiver to receive gases therefrom, absorbing liquid conduit means in communication with the absorber and with said blow-down receiver so as to conduct liquid from the absorber to said receiver, separating means adapted to separate brous substance and cooking liquor, means for conducting said mixture from the blow-down receiver to the separating means, a plurality of evaporators each having an evaporating zone, concentrate conduit means for connecting said evaporators in series so that concentrate is conducted from one evaporator to the evaporating zone of the next succeeding evaporator, a condenser communicating with each evaporator so as to receive condensible medium therefrom, said condensers being adapted for the passage of a condensing medium and a condensible medium in indirect heat exchange relationship with one another, vacuum producing means cooperating with each of the evaporators and condensers to maintain the same under vacuum and evaporate the liquor conducted to said evaporators, waste sulpl'ute liquor conducting means in communication with said separating means so as to receive separated liquor therefrom and in communication with the evaporating zone of the iirst of a series of evaporators to conduct said liquor thereto, concentrate receiving means, means in communication with the last of said series of evaporators and With the concentrate receiving means to conduct concentrate from said last evaporator to the receiving means, concentrate conducting means in communication with the concentrate receiving means and said condensers so as to conduct concentrate to said condensers for use as a condensing medium, other concentrate conducting means in communication with said concentrate receiving means and with the absorber so as to conduct concentrate to said absorber, condensate conducting meansy in communication with the condensers and with said separating means so as to conduct said condensate from the condensers to the separating means, and a used concentrate conduit in communication with the first of said series of evaporators and with the condensers so as to receive concentrate from said condensers after use as a condensing medium and conduct it to said first of the series of evaporators so as to receive said used concentrate after use thereof as a condensing medium in the condensers and to conduct it to the evaporating zone of said first evaporator.

9. In a sulphite pulp plant comprising a digester adapted to receive a fibrous substance, sulphite cooking liquor and steam, means for blowing down said digester, a blow-down receiver in communication with the digester to receive a mixture of fibrous material and cooking liquor therefrom, a blow-down vapor condenser in communication with the blow-down receiver so as to receive vapor therefrom, said blow-down vapor condenser being adapted to receive a condensing medium and a condensible medium for passage in indirect heat exchange relationship with one another, an absorber so arranged that a gas and a liquid are passed in contact with one another, a vgas line in communication with the absorber and with said blow-down vapor condenser so as to receive uncondensed vapor therefrom, absorbing liquid conduit means in communication with the absorber and with said blow-down receiver so as to conduct liquid from the absorber to said receiver, separating means adapted to separate fibrous substance and cooking liquor, means for conducting said mixture from the blow-down receiver to the separating means, a

19 plurality of evaporators each having an evaporating zone, concentrate conduit means for connecting said evaporators in series so that concentrate is conducted from one evaporator to the next evaporating zone of the succeeding evaporator, a condenser communicating with each evaporator so as to receive condensible medium therefrom, said last-mentioned condensers being adapted for the passage of a condensing medium and a condensible medium in indirect heat exchange relationship with one another, vacuum producing means cooperating with each of the evaporators and condensers to maintain the same under vacuum and evaporate the liquor conducted to said evaporators, waste sulphite liquor conducting means in communication with said separating means so as to receive separated liquor therefrom and in communication with the evaporating zone I" the first of a series of evaporators to conduct said liquor thereto, concentrate receiving means, means in communication with the last of said series of evaporators and with the concentrate receiving means to conduct concentrate from said last evaporator to the receiving means, concentrate conducting means in communication with the concentrate receiving means and said condensers so as to conduct concentrate to said condensers for use as a condensing medium, other concentrate conducting means in communication with said concentrate receiving means and With the blow-down vapor condenser, a connection between said b1owdown vapor condenser and said absorber arranged to conduct concentrate used as a condensing medium in said bloW-doWn vapor condenser to the absorber for use as absorbing liquid therein, a condensate line in communication with the blow-down condenser and with said separating means to conduct condensate from the condenser to the separating means for use as a separating fluid therein, and a used concentrate conduit in communication with the rst of said series of evaporators and with the condensers so as to receive concentrate from said condensers after use as a condensing medium and conduct it to said first of the series of evaporators so as to receive said used concentrate after use thereof as a condensing medium in the condensers and to conduct it to the evaporating zone of said rst evaporators.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,103,216 Moore et al July 14, 1914 1,263,486 Thorne Apr. 23, 191-8 1,308,184 McAfee July 1, 1919 1,469,958 Richter Oct. 9, 1923 1,864,619 Richter June 28, .1932 2,025,891 Paulson Dec, 3l, 1935 2,108,567 Scholier et al. Feb. 15, 1933 2,197,059 Seidel Apr. 16, 1940 2,238,456 Tomlinson Apr. 15, 1941 2,352,304 Young June 27, 1944 2,385,955 Tomlinson Oct. 2, 1945 OTHER REFERENCES Technical Association Papers, Series 16, pages 198-200, 1933; and Series 19, pages 285-292, 1936,

Pulp and Paper Mag. of Canada, vol. 50, October 1949, pp. 114-121. 

1. IN A SULPHITE PULP PLANT COMPRISING A STEAM GENERATOR, STEAM CONDUIT MEANS FOR CONDUCTING STEAM FROM THE STEAM GENERATOR, A DIGESTER ADAPTED TO RECEIVE A FIBROUS SUBSTANCE, SULPHITE COOKING LIQUOR AND STEAM FROM THE STEAM GENERATOR, MEANS FOR BLOWING-DOWN SAID DIGESTER, SEPARATING MEANS ADAPTED TO SEPARATE FIBROUS SUBSTANCE AND COOKING LIQUOR, MEANS FOR CONDUCTING THE MIXTURE BLOWN-DOWN FROM THE DIGESTER TO THE SEPARATING MEANS, A PLURALITY OF EVAPORATORS EACH HAVING AN EVAPORATING ZONE, CONCENTRATE CONDUIT MEANS FOR CONNECTING SAID EVAPORATORS IN SERIES SO THAT CONCENTRATE IS CONDUCTED FROM ONE EVAPORATOR TO THE EVAPORATING ZONE OF THE NEXT SUCCEEDING EVAPORATOR, A CONDENSER COMMUNICATING WITH EACH EVAPORATOR SO AS TO RECEIVE CONDENSIBLE MEDIUM THEREFROM, SAID CONDENSERS BEING ADAPTED FOR THE PASSAGE OF A CONDENSING MEDIUM AND A CONDENSIBLE MEDIUM IN INDIRECT HEAT EXCHANGE RELATIONSHIP WITH ONE ANOTHER, MEANS CONNECTING SAID CONDENSERS IN SERIES SO AS TO CONDUCT CONDENSING MEDIUM AFTER PASSAGE THEREOF IN SAID HEAT EXCHANGE RELATIONSHIP WITH SAID CONDENSIBLE MEDIUM IN ONE CONDENSER FROM THE ONE CONDENSER TO THE NEXT SUCCEEDING CONDENSER, VACUUM PRODUCING MEANS COOPERATING WITH EACH OF THE EVAPORATORS AND CONDENSERS TO MAINTAIN THE SAME UNDER VACUUM AND EVAPORATE THE LIQUOR CONDUCTED TO SAID EVAPORATORS, WASTE SULPHITE LIQUOR CONDUCTING MEANS IN COMMUNICATION WITH SAID SEPARATING MEANS SO AS TO RECEIVE SEPARATED LIQUOR THEREFROM AND IN COMMUNICATION WITH THE EVAPORATING ZONE OF THE FIRST OF A SERIES OF EVAPORATORS TO CONDUCT SAID LIQUOR THERETO, CONCENTRATE RECEIVING MEANS, MEANS IN COMMUNICATION WITH THE LAST OF SAID SERIES OF EVAPORATORS AND WITH THE CONCENTRATE RECEIVING MEANS, CONCENTRATE CONDUCTING MEANS IN COMMUNICATION WITH THE CONCENTRATE RECEIVING MEANS AND THE FIRST OF A SERIES OF SAID CONDENSERS SO AS TO CONDUCT THE CONCENTRATE TO SAID FIRST CONDENSER FOR USE AS A CONDENSING MEDIUM THEREIN, AND A USED CONCENTRATE CONDUIT IN COMMUNICATION WITH THE LAST OF SAID SERIES OF CONDENSERS AND THE FIRST OF SAID SERIES OF EVAPORATORS SO AS TO RECEIVE SAID USED CONCENTRATE AFTER USE THEREOF AS A CONDENSING MEDIUM IN SAID LAST CONDENSER AND TO CONDUCT IT TO THE EVAPORATING ZONE OF SAID FIRST EVAPORATOR. 